The present invention relates generally to injection molding, and, more specifically, to vacuum initiated injection molding of solder or plastic for example.
Standard injection molding uses positive pressure to force a liquid with low viscosity into mold cavities. The injected liquid displaces the gas or air in the mold cavities and is then allowed to solidify for forming the desired molded article. If the mold cavity is large, or if the cavity is open at two places, then displaced gas can easily flow out a vent. However, a tiny cavity with a single opening, or blind hole, presents special difficulties. For solder molding when the cavity diameter is quite small, such as 10-750 microns, then it is very difficult or impractical to include a vent. This is especially true in a array of mold cavities with cavity separation as small as about 75 microns. Such blind hole mold cavities will trap gas therein preventing complete filling of the cavity with the injected liquid resulting in defective molded articles. And, since the injection pressure exceeds ambient or atmospheric pressure, undesirable leakage of the injected liquid in the injection apparatus may occur.
Vacuum casting and vacuum-initiated blow-molding solve some of these problems. However, these methods typically require sophisticated valves and are limited as to mold sizes and types. The molds are typically injected one at a time in a sequential process which seals the liquid reservoir to each mold cavity in turn. After a temporary seal is made, valves sequentially introduce vacuum and liquid into the mold cavity.